Linear vibration generation device

ABSTRACT

Disclosed is a linear vibration generating device including: a stator including a bracket on which a coil is seated, and a case made of a magnetic material which is engaged to the bracket to form an inner space; a vibrator including a permanent magnet for generating a vibration force in cooperation with the coil, and a weight enclosing a circumference of the permanent magnet; a resilient member which is positioned between the vibrator and the stator to resiliently support vertical oscillation of the vibrator; and a plate which is positioned between the resilient member and the vibrator

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional Application of U.S. Ser. No. 15/049,569filed on Feb. 22, 2016, which is a continuation of InternationalApplication No. PCT/KR2014/010576 filed on Nov. 5, 2014, which claimspriority to Korean Application No. 10-2013-0134890 filed on Nov. 7,2013, which applications are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a linear vibration generating device,and more particularly, to a linear vibration generating device capableof generating a vibration by use of repeatedly vertically linearmovement of a weight which is caused by interaction between an electricfield generated by a coil and a magnetic field generated by a permanentmagnet.

BACKGROUND ART

Due to the popular propagation of cellular phones, noise pollutioncaused by incoming call ringtone leads to introduction of a new type ofsilence incoming call, such as vibration. Such a new type of silenceincoming call is realized by a technology of notifying a user of theincoming call or reception of a text message by applying anelectromagnetic force to a weight to vibrate the weight.

The incoming call notification of the vibration type according to therelated art generally employs a technology of eccentrically mounting arotating vibrator to a motor. The above technology has drawbacks in thatit does not guarantee an extended lifespan, the speed of response is notfast, and it is limited to various vibration modes. Accordingly, withthe trend in rapid popularization of a smartphone of a touch type,referred to as a touch phone, it is limited to meet the demand of users.

In order to solve the above problems, a linear vibration generatingdevice has been proposed to generate vibration by linearly oscillating aweight. The proposed linear vibration generating device is configured togenerate the desired vibration by linearly oscillating the weight withinteraction between an electric field caused by a coil, to which acurrent is applied, and a magnetic field caused by a permanent magnetenclosing the coil.

Korea Patent No. 1254211 (Published on Apr. 18, 2013, entitled “LinearActuator”, hereinafter referred to as the related patent document)discloses a technology of generating the vibration by linearlyoscillating the weight. The technology disclosed in the related patentdocument is to maintain stable operation characteristics by increasingmagnetic efficiency and to miniaturize the device.

The linear actuator disclosed in the related patent document will now bedescribed in detail with reference to FIG. 1.

Referring to FIG. 1, the linear actuator includes a vibrator 115, astator 110, and cases 135 and 102 for protecting the vibrator and thestator. The vibrator 115 has a magnet 111 for producing the magneticfield and a weight 112 enclosing the magnet. The stator 110 has a yoke107 installed at a center of the lower case 102 and a coil 106 disposedaround the yoke 107.

A PCB 105 is disposed at a center of a top surface of the lower case 102so as to be electrically connected to the coil 106 and thus transmit anelectric signal to the coil from the exterior. An elastic member 120 isinterposed between the upper case 135 and the weight 112, or the lowercase 102 and the weight 112 to elastically support the vibrator 115 andlimit an amplitude of vibration within a desired value.

In order to increase a magnetic flux density with the magnetic shield,an upper plate 113 and a lower plate 114 are provided to top and bottomsurfaces of the magnet 111 to in such a way of being brought intoclosely contact with each other to cover the upper and lower portions ofthe magnet 111, and dampers 140 and 142 are attached to one surface ofthe upper case 135 and one surface of the lower case 102 which face theplates 113 and 114, respectively.

The dampers 140 and 142 serve as a shock absorbing member capable ofpreventing the top and bottom surfaces of the vibrator 115 from cominginto contact with the cases 135 and 102 when the vibrator 115 oscillatesin the vertical direction. The dampers serving as the shock absorbingmember can reduce noise generated when the vibrator 115 comes intocontact with the cases 135 and 102.

According to the above related art, when the electric signal (AC power)is input to the coil 106 through the PCB 105, the vibrator 115vertically oscillates relative to the stator 110 by use of theinteraction between the electric field generated by the stator 110 andthe magnetic field generated by the magnet forming the vibrator 115.

However, the configuration disclosed in the related patent document hasthe following problems.

First, since the dampers are provided at inner upper and lower positionsof the case, and the plates 113 and 114 having a desired thickness areprovided on the top and bottom surfaces of the vibrator, it is not easyto secure a sufficient stroke distance, that is, an amplitude, so thatthe vibrator vibrates in the limited space of the case. As a result, theheight of the case should be increased, which does not meet theminiaturization of the device. Also, the above-described related art hasanother problems of producing noise due to collision between thevibrator and the case, and being limited to thinning of the actuator dueto the magnetic shield or the like.

Finally, in the process of generating vibrating the vibrator, since thevibrator undergoes lateral wobble, that is, pitching motion, as well asthe vertical oscillation, an outer corner of the vibrator comes intodirectly contact with the case, which causes the noise to produce,thereby deteriorating the quality and reliability of the product.

SUMMARY

Accordingly, the problem to be solved by the present invention is toprovide a linear vibration generating device capable of securing a spacewhich can obtain a sufficient stroke distance, that is, a sufficientamplitude, to cause a vibrator to oscillate without increasing a heightof a case, thereby miniaturizing the device.

Another problem to be solved by the present invention is to provide alinear vibration generating device capable of preventing mechanicalcontact of components due to a pitching motion of a vibrator, and thuseffectively decreasing a noise to be caused by the contact.

To accomplish the above-mentioned object, according to one aspect of thepresent invention, there is provided a linear vibration generatingdevice including: a stator including a bracket on which a coil isseated, and a case made of a magnetic material which is engaged to thebracket to form an inner space; a vibrator including a permanent magnetfor generating a vibration force in cooperation with the coil, and aweight enclosing a circumference of the permanent magnet; a resilientmember which is positioned between the vibrator and the stator toresiliently support vertical oscillation of the vibrator; and a platewhich is positioned between the resilient member and the vibrator.

The linear vibration generating device may further include a dampingmember which is provided on at least one surface of an exposed surfaceof the permanent magnet which is opposite to the plate, and one surfaceof the stator facing the exposed surface of the permanent magnet.

The damping member provided on the exposed surface of the permanentmagnet may include a magnetic fluid.

The plate covers a portion of the weight, and an inner peripheralsurface of the plate further may protrude inwardly from an innerperipheral surface of the permanent magnet, or be positioned on the sameline as the inner peripheral surface of the permanent magnet.

Preferably, an inner peripheral surface of an inner fixing end of theresilient member which is brought into contact with the plate isarranged on the same line as an inner peripheral surface of the plate.

In one embodiment of the present invention, the stator may furtherinclude a yoke housed in an inner diameter portion of the coil.

The yoke may be made of a magnetic material, and be formed in acylindrical shape having a T- or cross-shaped cross section.

In one embodiment of the present invention, the linear vibrationgenerating device may further include a magnetic fluid which is appliedon an outer surface of the plate.

One end (inner fixing end) of the resilient member may be fixed to theplate, and the other end (outer fixing end) may be fixed to one side ofthe case or a top surface of the bracket facing the plate.

In another embodiment of the present invention, the linear vibrationgenerating device may further include a pitching impact protector whichis provided on the weight facing the weight which is opposite to theplate.

In this instance, an edge or a corner of a top surface of the weight maybe provided with a recessed portion to correspond to the pitching impactprotector.

According to embodiments of the present invention, even though the plateis installed to any one of the top and bottom surfaces of the vibratorto which the resilient member is attached, it is possible tosufficiently concentrate the magnetic flux of the permanent magnet,thereby realizing the linear vibration generating device having theeffective vibration performance. Also, it is possible to reduce thecosts and the size by eliminating the plate.

Specifically, as compared to the configuration of the related art inwhich the plates are provided on both the upper and lower portions ofthe permanent magnet, the plate can be provided on only any one of theupper and lower portions by applying the case made of the magneticmaterial. Accordingly, the linear vibration generating device can securethe space which can obtain the sufficient stroke distance, that is, thesufficient amplitude, to cause a vibrator to oscillate withoutincreasing the height of the case, thereby improving the performance andminiaturizing the device. In addition, the present invention includesthe damping member made of the magnetic fluid which is directly appliedon the surface of the permanent magnet, it is possible to minimizedislocation of the damping member which is positioned at a point towhich impact is heavily applied.

The plate inner peripheral surface of the plate further protrudesinwardly from the inner peripheral surface of the permanent magnet or ispositioned on the same line as the inner peripheral surface of thepermanent magnet. In addition, the inner surface of the plate isarranged on the same line as the inner peripheral surface of the onefixing end of the resilient member. Therefore, it is possible tomaximize the length of the driving portion (referred to as a springfoot) of the resilient member which connects the outer fixing end andthe inner fixing end of the resilient member.

Specifically, even though the driving portion (spring foot) of thespring does not have the complicated structure, unlike that of therelated art, the resilient member can have the desired restoring force.After all, it is possible to simplify the configuration of the resilientmember, thereby having the competitive price due to the improved massproduction and the reduced manufacturing costs.

Also, by the damper provided on one surface of the case facing the outercorner of the weight, it is possible to prevent mechanical contact ofcomponents (weight and stator) due to a pitching motion of the vibratorand reduce the noise caused by the mechanical contact. Accordingly, thepresent invention can realize the linear vibration generating device ofhigh reliability and high quality which can show stable vibrationcharacteristics.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a linear vibration generating deviceaccording to the related art.

FIG. 2 is an exploded perspective view of a linear vibration generatingdevice according to a first embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating an assembled state of thelinear vibration generating device in FIG. 2.

FIG. 4 is a cross-sectional view illustrating a modified embodiment ofthe first embodiment in FIG. 3.

FIG. 5 is a cross-sectional view illustrating another modifiedembodiment of the first embodiment in FIG. 3.

FIG. 6 is an exploded perspective view of a linear vibration generatingdevice according to a second embodiment of the present invention.

FIG. 7 is a cross-sectional view illustrating an assembled state of thelinear vibration generating device in FIG. 6.

FIG. 8 is a cross-sectional view illustrating a modified embodiment ofthe second embodiment in FIG. 7.

FIG. 9 is a cross-sectional view illustrating another modifiedembodiment of the second embodiment in FIG. 7.

FIGS. 10 and 11 are cross-sectional views illustrating a linearvibration generating device according to third and fourth embodiments ofthe present invention.

DETAILED DESCRIPTION

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

FIG. 2 is an exploded perspective view of a linear vibration generatingdevice according to a first embodiment of the present invention. FIG. 3is a cross-sectional view illustrating an assembled state of the linearvibration generating device in FIG. 2. The whole configuration of thelinear vibration generating device according to the present inventionwill now be described with the drawings.

Referring to FIGS. 2 and 3, the linear vibration generating deviceaccording to the present invention mainly includes a vibrator 10 and astator 20. A resilient member 40 is interposed between the vibrator 10and the stator 20 to resiliently support vertical oscillation of thevibrator 10, and a PCB 50 for supplying an AC power to generate theoscillation is provided on a planar bracket 34 constituting the stator20.

The vibrator 10 has a permanent magnet 12 for forming a magnetic fieldand a weight 13 engaged to the permanent magnet 12 in such a manner ofenclosing the permanent magnet 12 to apply a load to the permanentmagnet. The stator 20 has the bracket 34, a cylindrical coil 22 seatedon a top surface of the bracket 34 and placed at a center of thepermanent magnet 12, a yoke 24 housed in an inner diameter portion ofthe coil 22, and a case 30.

The coil 22 is electrically connected to the PCB 50 placed on thebracket 34, and receives the electric signal to vibrate the vibrator 10relative to the stator 20. The vibrator 10 vertically oscillatesrelative to the stator 20 by an attractive force and a repulsive forcebetween the electric field generated by the coil 22 and the magneticfield generated by the permanent magnet 12 in response to the receivedelectric signal.

An amplitude of the vibrator 10 can be limited within a proper range bya coefficient of elasticity of the resilient member 40 and theattractive force acting between the permanent magnet 12 and the Yoke 24.The permanent magnet 12 has an inner diameter to such an extent not asto interfere the yoke 24, and may be formed in an annular shape havingopposite polarities in a vertical direction, that is, a donut shape.

The yoke 24 may be formed in a simple cylindrical shape, or may beformed in a cylindrical shape having a T- or cross-shaped cross section.In the case of the latter, the yoke has a planar shield to cover anupper portion of the coil 22. In particular, the yoke 24 is made of amagnetic material to concentrate the magnetic flux generated from thepermanent magnet 12 on the coil 22 wound around the yoke, and to producethe attractive force with the permanent magnet, thereby limiting theamplitude of the vibrator 10. The yoke 24 which is formed in acylindrical shape having a T cross section is not contact with the case30. Namely the yoke 24 is spaced with upper portion of case 30.

In view of the effect of concentrating the magnetic flux through themagnetic shield or weight lightening, the yoke is preferably formed tohave the T-shaped cross section. Also, in view of the easy of assemblywhen the yoke is held in the process of transferring the yoke of a verysmall size to an object to be assembled, the yoke is preferably formedto have the cross-shaped cross section.

The linear vibration generating dev ice further includes a plate 16 tocover a portion of the vibrator 10, as well as the bottom surface of thepermanent magnet 12. The plate 16 may have a planar body with a holeformed in a center thereof. The plate 16 serves as the magnetic shieldin order to concentrate the magnetic flux generated from the permanentmagnet 12 on the coil 22.

The plate 16 is fixed to one side of the vibrator 10 facing theresilient member 40, and thus vibrates together with the permanentmagnet 12 and the weight 13 when the vibrator 10 vertically oscillates.The plate 16 covers a portion of the weight 13, and an inner peripheralsurface 12 of the plate may further protrude inwardly from an innerperipheral surface 11 of the permanent magnet 12 or be positioned on thesame line as the inner peripheral surface 11 of the permanent magnet 12in a vertical direction.

The resilient member 40 resiliently supports the vibrator 10 consistingof the permanent magnet 12 and the weight 13 to provide the vibratorwith a resilient force, which returns the vibrator to its originalposition relative to the stator 20, and to limit the amplitude of thevibrator 10, which prevents the vibrator 10 consisting of the permanentmagnet 12 and the weight 13 from colliding against the case 30constituting the stator 20.

One end of the resilient member 40 is welded to the bottom surface ofthe plate 16, and an opposite end is welded to an edge of the topsurface of the bracket 34. Of course, both ends of the resilient membermay be welded to the top surface of the plate and one surface of theupper case facing the top surface in the configuration of which theplate is placed on the top surface of the vibrator (see the secondembodiment described later), respectively.

If an inner peripheral surface 13 of an inner fixing end 44 of theresilient member 40 which is brought into contact with the plate 16 isarranged on the same line as an inner peripheral surface 12 of the plate16, it is possible to maximize the length of a driving portion (referredto as a spring foot 43) of the resilient member which connects an outerfixing end 42 and the inner fixing end 44 of the resilient member 40 inthe limited space, thereby simplifying a pattern of the driving portion43.

The linear vibration generating device with no plate 16 can be easilythinned, but there is a problem in that the driving portion 43 of theresilient member 40 is not positioned to be brought into directlycontact with the lower portion of the permanent magnet in the innermostside of the vibrator 10 relative to the inner diameter of the vibrator.

That is, the control of the amplitude (oscillation frequency orresonance frequency) of the resilient member 40 is advantageous as theresilient member is positioned in the innermost side of the vibratorrelative to the inner diameter of the vibrator. However, if theresilient member is directly welded to the permanent magnet, thepermanent magnet is demagnetized to change the vibration force.According to the present invention, since the plate 16 is positionedonly between the resilient member 40 and the permanent magnet 12, thelinear vibration generating device can be provided of which thevibration characteristic is not deteriorated while reducing thethickness thereof.

The case 30 constituting the stator 20 is engaged to the bracket 34 toform an inner space in which the vibrator 10 and the resilient member 40are housed. In the embodiment of the present invention, as long as amaterial of the case 30 is magnetic (for example, metal material), it isnot limited to any specific material. The case may be formed to have awidth and a height such that the vibrator, the resilient member, and thecoil can be housed therein.

The PCB 50 inputs the electric signal to the coil 22 from the exterior,and, to this end, is electrically connected to a coil wire led from thecoil 22. The PCB 50 may be provided as a ring shape, as illustrated inFIG. 2, and be fixed by the yoke 24 housed in the inner diameter portionof the coil 22 which is brought into directly contact with the bracket34 or is engaged to an engaging hole formed in the center of the bracket34.

In order to prevent the direct contact between the vibrator and the casewhen the vibrator 10 vertically oscillates, according to the firstembodiment, a damping member 60-1 is provided on the exposed surface ofthe permanent magnet 12 which is positioned opposite to the attachedside of the plate 16. In this embodiment, the damping member may be amagnetic fluid which is directly applied on the exposed surface of themagnet and is restrained from leaving from its location by the magneticforce. That is, since leaving of the damping member 60-1 is minimized bythe direct influence of the permanent magnet, the reliability of theproduct is advantageously improved.

As illustrated in FIG. 4 which shows a modified embodiment of the firstembodiment in FIG. 3, a damping member 60-2 may be attached to one sideof the case 30 which faces the exposed surface of the permanent magnet12 which is opposite to the plate 16. In this instance, the dampingmember 60-2 may employ a damper made of rubber, silicon or foam rubber.

As illustrated in FIG. 5 showing another modified embodiment, dampingmembers 60-3 and 60-4 may be provided on both the exposed surface of thepermanent magnet 12 which is opposite to the plate 16 and the side ofthe case 30 facing the exposed surface. In this instance, it ispreferable that a magnetic fluid is employed as the damping member 60-3of the exposed surface, and a damper made of a rubber or siliconmaterial is employed as the damping member 60-4 of the side facing theexposed surface.

In the first embodiment illustrated in FIGS. 2 to 5, a reference numeral19 denotes the magnetic fluid applied on the outer peripheral surface ofthe plate 16, which covers a portion of the lower portion of thevibrator 10, for the purpose of the magnetic shield, and 70 denotes ashock absorbing member which is disposed on the bracket 34 in theresilient member 40 to prevent the mechanical contact between thebracket 34 and the resilient member 40 resiliently deformed when thevibrator 10 vertically oscillates.

The shock absorbing member 70 may be made of a material capable ofabsorbing or alleviating the shock when the vibrator 10 comes intocontact with the shock absorbing member, for example, rubber, silicon orfoam rubber, but it is not limited to any special material as long asthe material realizes the shock absorption with cushion. As illustratedin the drawing, the shock absorbing member may be provided in an annularshape.

FIG. 6 is an exploded perspective view of a linear vibration generatingdevice according to the second embodiment of the present invention. FIG.7 is a cross-sectional view illustrating an assembled state of thelinear vibration generating device in FIG. 6.

The linear vibration generating device according to the secondembodiment in FIGS. 6 and 7 is similar to the linear vibrationgenerating device according to the first embodiment, except that theplate 18 and the resilient member 40 are placed on the vibrator 10.Specifically, the plate 18 and the resilient member 40 are positioned onthe vibrator 10, and the exposed surface of the permanent magnet 12which is opposite to the plate 18 faces the bottom side.

Since the configuration of the second embodiment is substantiallysimilar to that of the first embodiment, except that the vibrator 10 andthe resilient member 40 are inverted in the case 30, the same componentsas those in the first embodiment are denoted by the same referencenumerals, and the detailed description will be omitted herein.Therefore, only components different from those in the first embodimentwill now be described in brief.

Referring to FIGS. 6 and 7, the linear vibration generating deviceaccording to the second embodiment includes a plate 18 which isconfigured to cover a portion of the vibrator 10, as well as the topsurface of the permanent magnet 12. The resilient member 40 isinterposed between the plate 18 and the stator 20, specifically, thecase 30, to resiliently support the vertical oscillation of the vibrator10.

The plate 18 is fixed to one surface of the vibrator 10 facing theresilient member 40, and thus vibrates together with the permanentmagnet 12 and the weight 13 when the vibrator 10 vertically oscillates,similar to the first embodiment. The plate 18 covers a portion of theweight 13, and an inner peripheral surface 12 of the plate may furtherprotrude inwardly from an inner peripheral surface 11 of the permanentmagnet 12 or be positioned on the same line as the inner peripheralsurface 11 of the permanent magnet 12 in a vertical direction.

One end of the resilient member 40 is fixed to the top surface of theplate 18, and an opposite end is fixed to one side of the case 30 facingthe plate 18. Similar to the first embodiment, if an inner peripheralsurface 13 of an inner fixing end 44 of the resilient member 40 which isbrought into contact with the plate 18 is arranged on the same line asthe inner peripheral surface 12 of the plate 18, it is possible topreferably maximize the length of a driving portion (referred to as aspring foot 43) of the resilient member.

A damping member 80-1 is provided on the exposed surface of thepermanent magnet 12 which is positioned opposite to the attached side ofthe plate 18, so as to prevent the mechanical contact between the lowerportion of the vibrator 10 and a base 34 when the vibrator 10 verticallyoscillates. In the second embodiment, the damping member 80-1 may be amagnetic fluid which is provided in such a way a center to be broughtinto contact with the case is convex in a downward direction.

According to a modified embodiment illustrated in FIG. 8, a dampingmember 80-2 may be a damper made of rubber, silicon or foam rubber whichis provided on the case facing the exposed surface of the permanentmagnet which is opposite to the plate 18, specifically, the top surfaceof the bracket 34. Otherwise, as illustrated in FIG. 9 showing anothermodified embodiment, damping members 80-3 and 80-4 may be provided onboth the exposed surface of the permanent magnet 12 which is opposite tothe plate 18 and the side of the case 30 facing the exposed surface.

In the above modified embodiment in FIG. 9 in which the damping members80-3 and 80-4 are provided on both the exposed surface of the permanentmagnet 12 and the side of the case 30, a magnetic fluid is employed asthe damping member 80-3 provided on the exposed surface, and a dampermade of a rubber or silicon material is employed as the damping member80-4 of the side of the case 30 facing the exposed surface.

According to the first and second embodiments of the present invention,even though the plate is installed to any one of the top and bottomsurfaces of the vibrator to which the resilient member is attached, itis possible to sufficiently concentrate the magnetic flux of thepermanent magnet, thereby realizing the linear vibration generatingdevice having the effective vibration performance. Also, it is possibleto reduce the costs and the size by eliminating the plate.

Specifically, as compared to the configuration of the related art inwhich the plates are provided on both the upper and lower portions ofthe permanent magnet, the plate can be provided on only any one of theupper and lower portions by applying the case made of the magneticmaterial. Accordingly, the linear vibration generating device can securethe space which can obtain the sufficient stroke distance, that is, thesufficient amplitude, to cause a vibrator to oscillate withoutincreasing the height of the case, thereby improving the performance andminiaturizing the device.

The plate inner peripheral surface of the plate further protrudesinwardly from the inner peripheral surface of the permanent magnet or ispositioned on the same line as the inner peripheral surface of thepermanent magnet. In addition, the inner surface of the plate isarranged on the same line as the inner peripheral surface of the onefixing end of the resilient member. Therefore, it is possible tomaximize the length of the driving portion (referred to as spring foot)of the resilient member which connects the outer fixing end and theinner fixing end of the resilient member in the limited space, therebysimplifying the configuration of the driving portion and providing thesufficient resiliently restoring force.

Meanwhile, FIGS. 10 and 11 are cross-sectional views illustrating alinear vibration generating device according to the third and fourthembodiments of the present invention.

As illustrated in FIGS. 10 and 11, the linear vibration generatingdevices according to the third and fourth embodiments of the presentinvention are substantially identical to those according to the firstand second embodiments, except that pitching impact protectors 90 and 92are provided on the stator 20 facing the weight 13 opposite to theplates 16 and 18, thereby preventing the vibrator 10 from being shockeddue to pitching motion.

In the third and fourth embodiments, one edge or corner of the weight 13is preferably further provided with recessed portions 14 and 15corresponding to the pitching impact protectors 90 and 92. If therecessed portions 14 and 15 are provided, it is possible to solve aproblem of losing the amplitude as much as the height of the pitchingimpact protectors 90 and 92 which are provided in the limited space.

While the present invention has been described with reference to theparticular illustrative embodiments, it is not to be restricted by theembodiments but only by the appended claims. It is to be appreciatedthat those skilled in the art can change or modify the embodimentswithout departing from the scope and spirit of the present invention.

The linear vibration generating device according to the presentinvention can be applied as an incoming call device for a cellularphone.

The invention claimed is:
 1. A linear vibration generating devicecomprising: a stator including a bracket on which a coil is seated, anda case made of a magnetic material which is engaged to the bracket toform an inner space; a vibrator including a permanent magnet forgenerating a vibration force in cooperation with the coil, and a weightenclosing a circumference of the permanent magnet; a resilient memberwhich is positioned between the vibrator and the stator to resilientlysupport vertical oscillation of the vibrator; a plate which ispositioned between the resilient member and a bottom surface of thevibrator; and a damping member which is directly provided on centralparts of an exposed surface of the permanent magnet which is opposite tothe plate to prevent the permanent magnet from contacting an upper partof the case.
 2. The linear vibration generating device according toclaim 1, wherein the damping member directly provided on the exposedsurface of the permanent magnet includes a magnetic fluid.
 3. The linearvibration generating device according to claim 2, wherein the platecovers a portion of the weight, and an inner peripheral surface of theplate further is positioned on the same line as an inner peripheralsurface of the permanent magnet.
 4. The linear vibration generatingdevice according to claim 2, further comprising a yoke housed in aninner diameter portion of the coil.
 5. The linear vibration generatingdevice according to claim 4, wherein the yoke is made of a magneticmaterial, and is formed in a cylindrical shape having a T-shaped crosssection and is not contact with the case.